Question

我为接收字符串的字段做了自定义属性。然后，我在枚举中使用custom属性。我需要从FieldAttribute中获取“ MyMethod”的结果，但它不会返回字符串

这就是我所拥有的：

枚举和属性：

public enum CustomEnum
{
    [Field("first field")]
    Field1,
    [Field("second field")]
    Field2,
    [Field("third field")]
    Field3
}

[AttributeUsage(AttributeTargets.Field)]
public class FieldAttribute : Attribute
{
    private string name;

    public FieldAttribute(string name)
    {
        this.name = name;
    }

    public string LastName { get; set; }

    public string MyMethod()
    {
        return this.name + this.LastName;
    }
}

用法：

public class Program
{
    public static void Main(string[] args)
    {
        PrintInfo(typeof(CustomEnum));
    }

    public static void PrintInfo(Type t)
    {
        Console.WriteLine($"Information for {t}");
        Attribute[] attrs = Attribute.GetCustomAttributes(t);

        foreach (Attribute attr in attrs)
        {
            if (attr is FieldAttribute)
            {
                FieldAttribute a = (FieldAttribute)attr;
                Console.WriteLine($"   {a.MyMethod()}");
            }
        }
    }
}

请帮忙!!!

Answer 1

它是这样的：

public static void PrintInfo(Type t)
{
    Console.WriteLine($"Information for {t}");

    var pairs =
        from name in t.GetEnumNames()
        let member = t.GetMember(name).Single()
        let attr = (FieldAttribute)member.GetCustomAttributes(typeof(FieldAttribute), false)
                      .SingleOrDefault()
        let text = attr.MyMethod()
        select (name, text);

    foreach (var (name, text) in pairs)
        Console.WriteLine($"{name} -> {text}");
}

说明：您在类型上使用GetCustomAttributes，但实际上需要确实为fields on the enum type的枚举常量。因此，您需要获取MemberInfo作为枚举常量并要求其属性。

对于真正古老的编译器，您可以使用简单的

public static void PrintInfo(Type t)
{
    Console.WriteLine($"Information for {t}");

    foreach (string name in t.GetEnumNames())
    {
        MemberInfo member = t.GetMember(name).Single();
        FieldAttribute attr =
            (FieldAttribute)member.GetCustomAttributes(typeof(FieldAttribute), false)
                      .SingleOrDefault();
        string text = attr.MyMethod();
        Console.WriteLine(name + " -> " + text);
    }
}

字段的自定义属性

1 个答案: